<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>固定窗口</title>
		<style>
			body{
				height: 50000px;
				width: 10000px;
			}
			#ask{
				height: 160px;
				width: 100px;
				overflow: hidden;
				border: 1px solid red;
				position: fixed;
				left: 0;
				top: calc(50% - 50px);
			}
		</style>
	</head>
	<body>
		<div id="ask">
			<a href="#">
				<img src="../images/full_ask.png"/>
			</a>
		</div>
	</body>
</html>